Switched-mode power supply (SMPS) converters are widely used in various electronic applications ranging from telecommunication equipment to automobiles. The SMPS system offers advantageous power conversion efficiency and increased design flexibility over linear regulators.
One challenge of SMPS design is managing power loss due to switching losses. One way to reduce such switching losses is to use gallium nitride GaN power devices instead of silicon-based transistors to implement switching transistors. The low parasitic capacitance and lower on-resistance of GaN power devices reduce switching losses compared to traditional silicon-based transistors. As such GaN power devices are increasingly being used to implement compact power chargers for portable electronic devices.
Another challenge of SMPS design, especially with respect with power circuits used in low-power, portable devices, is managing the start-up behavior of the SMPS. Since chargers for low-power portable devices typically do not include an auxiliary power supply, power produced by the SMPS itself is often used to supply power to the circuit that controls the various active switching components of the SMPS. One way to deal with this issue is to use power from AC line input to power the control circuitry during start-up of the SMPS. In some systems a high-ohmic resistor coupled to the AC line input is used to charge an input capacitor coupled to the control circuit. Such circuits, however, may continue to draw power from the AC line input when the SMPS is not operating and/or is in a standby mode, which may conflict with the extremely low standby power requirements of some portable device charging systems.